Narrated `Abdullah bin Az-Zubair:
A group of Bani Tamim came to the Prophet (and requested him to appoint a governor for them). Abu Bakr said, "Appoint Al-Qaqa bin Mabad." `Umar said, "Appoint Al-Aqra' bin Habeas." On that Abu Bakr said (to `Umar). "You did not want but to oppose me!" `Umar replied "I did not intend to oppose you!" So both of them argued till their voices grew loud. So the following Verse was revealed: 'O you who believe! Be not for ward......' (49.1) (DE)
USC-MSA web (English) reference: Vol. 6, Book 60, Hadith 370 (DE)
Arabic reference (DE): Book 65, Hadith 4847 (DE)